Which of the following structures form the bulk of each of the testis?

a. Exchanging of gas: Alveoli are the primary sites for gas exchange in the lungs, where oxygen is absorbed into the blood and carbon dioxide is expelled.

b. Removing pathogens that are breathed in: This is a function of the respiratory tract's immune components, like macrophages in the alveoli, but not the primary function.

c. Containing mucus-producing goblet cells: Goblet cells are found in the respiratory tract but not in the alveoli.

d. Secreting surfactant to reduce surface tension: Alveolar cells do secrete surfactant, which is crucial for reducing surface tension and preventing alveolar collapse, but the primary function is gas exchange.

a. I, IV, and VII: Cranial nerve I (Olfactory) is involved in the sense of smell, not eye movement. Cranial nerve VII (Facial) controls facial expressions, not eye movement. Cranial nerve IV (Trochlear) does control one of the extraocular muscles.

b. V and V: This is not a valid option, as it repeats the same cranial nerve. Cranial nerve V (Trigeminal) is involved in facial sensation and chewing, not eye movement.

c. IV and V: Cranial nerve IV (Trochlear) is involved in eye movement, but cranial nerve V (Trigeminal) is not.

d. III, IV, and VI: Correct. Cranial nerve III (Oculomotor), cranial nerve IV (Trochlear), and cranial nerve VI (Abducens) all control the extraocular muscles responsible for eye movements.